Process of concentrating nitric acid.



I". C. ZEISBERG.

PROCESS 0F CONCENTRATING NITRIC ACID.

APPLICATION FILED OCT. I5. 1914.

Paentedbept. 5, 1916,

I I I FRED C. ZEISBERG, OF WILMINGTON, DELAWARE, ASSIGNOR. TO E. I. DUPONT Dr: NEMOURS POWDER COMPANY, OF WILMINGTON, DELAWARE, A CORPORA-TION OF NEW JERSEY.

PROCESS OF CONCENTRATIN G NITRIC ACID.

Specification of Letters Patent.

Patented Sept. 5, 1916..

Application filed October 15, 191A. Serial No. 866,781.

To all whom it may concern Be it knownl that I, FRED C. ZEISBERG, ofWilmington, in the county of New Castle,

and in the State of Delaware, have invented to a method for theseparation of nitric and sulfuric acids.

Hitherto ithas been found that when concentrating weak, nitric acid bymixing it with a dehydrating agent as, for example, sulfuric acid, anddistilling thermixture, the iirst portions of the distillate containstrong nitric acid but the later portions contain a considerable amountof water so that if all of the ldistillate is recovered together, andwithout separating the different portions, a rather weak distillate isobtained. It has therefore been customar to obtain the latter portionsof the distilfate separately from the first portions, and after mixingthe same with sulfuric acid, to redistil the nitric acid mixture toobtain a more concentrated nitric acid. *l

The object of my invention is to avoid the necessity of separating thedifferent portions ofl the distillate and to provide a continuousprocess in which a highly` concentrated nitric acid may be obtained. Y

A further object of my invention is t provide a process of the abovecharacter in which there' is only a very small amount of decompositionof the nitric acid.

A further object is to bring about the con` cent'ration of nitric acidin the presence of a dehydrating agent -without the necessity ofintroducing any water other than that contained in the nitric acid andthe dehydrating agent.

A still further object is to utilize the vapors of the dehydrating agentto assist in the dehydration of the nitric acid.

While my invention is capable of embodiment in many different forms, forthe purl pose of illustration I shall describe only oneform, and whileit is capable of being carried out in many different forms of apparatus,I have shown only one form thereof in the accompanying drawings, inwhich the figure is a diagrammatic representation of an apparatus thatmay be used for carrying out my invention.

In the drawings I have shown a still 1` which has a draw-olf pipe 2 atits side for drawing off the sulfuric acid that accumulates in thestill. At the top of the still 1. there is a column 3 filled with anysuitable illingmaterial 3, such as pumice stone, the same being retainedin place by being supported upon a perforated plate 4c located in thebottom of the column. At the top of the column 3 there is an inlet pipe5 for mixed nitric and sulfuric acids, said pipe 5 having a stop-cock 6and being connected to4 a tank 7 which contains the supply'of mixedynitric and sulfuric acids. From the top of the column 3 appe 8 conductsthe vaporized nitric acid to a condenser 9 located 1n a container 10 forcirculating a current of cold water around the coil. Said coil 9 has 'anoutlet pipe 11 for discharging the condensed nitric acid into areceptacle 12. The container 10 is provided with a valved cold watersupply pipe 13 and a discharge water pipe 14. From the coil 9 a pipe l5.leads to the bottom of a tower 16 which contains any suitable fillingmaterial, and which is provided witha valved water supply pipe 17 forsupplying a current of water within the tower 16, which absorbs thelower oxids of lnitrogen that-.pass out of the coil 9. The

water, with its dissolved oxids of nitrogen, passes out of the tower 16by means of a -aoI pipe 18 and is collected in a receptacle 19.

Any gases which are not absorbed in the column 16 may escape out of apipe 20 located at the top of the column 16. A water supply pipe 21provides a supply of water for the pipes 13 and 17.

In carrying out my process, the still '1 is filled with sulfuric acid ofany convenient strength as, for example, 80%, and is heated until theacid is boiling vigorously. When this occurs, a mixture of sulfuric andnitric acids is allowed yto flow downwardly from the tank 7, or saidacids are separately introduced into the column 3 where the acid mixturemeets the ascending vapors from the introduced at the same level in thecolumn 3. As a result the vapors are condensed and the heat given up bythe condensing vapors drives out the nitric acid, which ascends in thecolumn freed from any water vapor, and finally passes out of the columnthrough the pipe 8 as strong nitric acid vapor. The vapors are thenconducted to the coil 9 where the nitric acid vapor is condensed andfrom which it is collected in the receptacle 12. The small amounts oflower oxids of nitrogen resulting from the unavoidable decomposition ofsome of the nitric acid in the distillation are absorbed by the currentof water in the tower 16. The weak acid solution flowing out of thetower 16 is collected in the receptacle 19. The dilute sulfuric acidwhich collects in the still 1 flows out from the same through the pipe 2from which it may be collected and concentrated in any suitable manner,but preferably while hot to avoid the loss of heat.

In this process practically all of the nitric acid is obtained in ahighly concentrated condition. In this process only a small percentageof lower oxids of nitrogen is produced, owing to the fact that thenitric acid, upon being vaporized, immediately ascends t0 a coolerportion of the apparatus, the temperature of the column 3 being suchthat it may be as low as 85o C. at the top. The

.product obtained is therefore of great utiltain a residual acid of anydesired strength. boiling solution of sulfuric aci ity, considering itshigh strength. In previous processes of obtaining nitric acid bydistilling the mixture of sulfuric and nitric acids, the amounts oflower oxids formed were much greater, owing to the fact that the nitricacid vapors came int-o contact with super-heated portions of the stilland 'were there decomposed. The process is easy to control as it is acontinuous one, and as it is merely necessary, in carrying out theprocess; to adjust the rate of flow of the incoming mixed acids.Furthermore, no Water need be introduced in the process other than thatcontained in the nitric and sul- ,furic acids introduced into thecolumn.

As one example of my process, I may operate the process with a mixtureof one part of 50% nitric acid and three parts of 90% sulfuric acid.Upon distilling this mixture in the apparatus above referred to, adistillate is obtained which has a total acidity of 100%. The residualsulfuric acid coming from the still 1 contains 77.6% sulfuric acid andless than .1% of nitric acid. The temperature of the top of the column 8may be about 86 C. and in the still about 200o C. It is to beunderstood, of course, that the above proportions and temperatures maybe largely varied without departing from the spirit of my invention.

It is possible, by changing the proportions and strengths of the acidsintroduced, to ob- While I have described my invention above in detail,I wish it to be understood that many changes may be. made thereinwithout departing from the spirit of my invention.

I claim:

1. The process which comprises passing nitric acid and a dehydratingagent into a chamber, and driving off the nitric acid from the same bybringing into contact therewith water vapors obtained from a boilingaqueous solution of said dehydrating agent.

2. The process which comprises passing sulfuric and nitric acids into achamber, and driving off the nitric acid from the same by bringing intocontact therewith vapors from a boiling solution of sulfuric acid,condensing the nitric acid vapors, and recovering the residual oxids ofnitrogen by absorbing the same in water.

3. The process which comprises continuously passing sulfuric and nitricacids into a chamber, and driving off the nitric acid from the same bybringing into contact therewith vapors from a boiling solution ofsulfuric acid, condensing the nitric acid vapors, and recovering theresidual oxids of nitrogen by absorbing the same in water.

4. The process which comprises continuously passing sulfuric and nitricacids into a chamber, and driving off the nitric acid from the same bybringing into contact therewith vapors from a boiling solution ofsulfuric acid, and continuously removing the diluted sulfuric acid,condensing the nitric acid vapors, and recovering the residual oxids ofnitrogen by absorbing the same in water.

5. The process of concentrating nitric acid which comprises passingnitric acid and a dehydrating agent into a chamber and driving off thenitric acid from the same by subjecting the nitric acid therein to theaction of water vapors obtained from weak nitric acid previouslyconcentrated by the same process.

- 6. The process of concentrating nitric acid which comprises passingnitric acid and sulfuric acid into a chamber and driving of the nitricacid from the same by subjecting the nitric acid therein to the actionof water vapors obtained from weak nitric acid previously concentratedby the same process.

7. The process which comprises passing sulfuric and nitric acids in theform of a liquid into a chamber, and driving off the nitric acid fromthe same by bringing into contact therewith vapors from a boilingsolution of sulfuric acid.

8. The process which comprises continuously passing sulfuric and nitricacids in the form of a liquid into a chamber and driving off the nitricacid from the same by bringing into contact therewith v anors from a intestimony that I claim the foregoing I have hereunto set my hand.

FRED C. ZEISBERG.

Witnesses:

P.' G. STRICHLAND, R. H. RAWLEIGH.

